Torsional and steric strain #3.9

[Isha Bagga 3J]

For question 9 in chapter 3 of the organic chemistry workbook, how do you know that there is torsional and steric strain? For the torsional strain, are the two CH2 parts eclipsed?

[martha-1I]

You can see that there is steric and torsional strain once you draw the lewis structure for molecules given. You will notice that the hydrogens in the H2C-CH2 are eclipsed and the carbon atoms are adjacent each other which gives it a torsional strain. When you move up on the molecule you will see that there are two hydrogens that want to occupy the same location which makes this interaction steric. I will post a picture of this to give you a visual in a coupe of minutes once I draw it.

[martha-1I]

Attached is a picture explaining why the unfavorable interactions in this question are steric and torsional.

[Chem_Mod]

Well done Martha!

[LeilaBushweller1F]

How do you know that the substituent groups are both on the top of the carbons, rather than opposite of each other (one on the top of a carbon, the other on the bottom)?

[Chem_Mod]

you need to draw Newmann projection througn C₂-C₃ axis to view it. When two large groups (CH₂F and CH₂CH₃) are eclipsed in the Newmann, you will observe the steric and torsional strain as Martha described.

[Justin Le 2I]

You can tell by looking at the Lewis structure. In this case, both of them are on top.